body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
}

.content {
    padding: 20px;
}

#backToTopBtn {
    width: 64px;
    height: 64px;
    display: none; /* 默认隐藏按钮 */
    position: fixed;
    bottom: 20px;
    right: 30px;
    z-index: 99;
    font-size: 18px;
    border: none;
    outline: none;
    /* background-color: #555; */
    background: url(./img/回到顶部.png) no-repeat;
    color: white;
    cursor: pointer;
    padding: 15px;
    border-radius: 4px;
}

#backToTopBtn:hover {
    /* background-color: #777; */
}